The invention is directed to a method and an apparatus for intradermal implantation of a device to facilitate non-invasive measurement of analytes including, but not limited to, glucose, cholesterol, lactate, bilirubin, blood gases (pO2, pCO2pH), urea, creatinine, phosphate, myoglobin, and hormones.
Diabetes mellitus is a chronic systemic disease characterized by disorders in the metabolism of insulin, carbohydrate, fat, and protein as well as in the structure and function of blood vessels. Currently, diabetes is a leading cause of death in the United States, and more than 16 million Americans are believed to have this disease. Intensive management of blood sugars through frequent monitoring is effective to prevent, or at least slow, the progression of diabetic complications such as kidney failure, heart disease, gangrene, and blindness.
Maintaining blood glucose levels near normal levels can only be achieved with frequent blood glucose monitoring so that appropriate actions can be taken, such as insulin injections, proper diet, or exercise. Unfortunately, the current method of sensing is a colorimetric/electro-enzymatic approach, which is invasive, requiring a finger stick to draw blood each time a reading is needed. This approach is both time-consuming and painful. Therefore, there is a lack of compliance among the diabetic population for even monitoring their levels once per day, which is far below the recommended five or more times daily.
Minimally invasive approaches have been investigated as a less painful method of estimating blood glucose concentrations. These approaches involve disruption of the skin barrier without puncturing a capillary to obtain a small sample of interstitial fluid for subsequent measurement of glucose concentration. Various methods have been used including electrical current, suction, penetration, and ultrasound for obtaining interstitial fluid samples. While measurement of glucose in interstitial fluid is potentially feasible, it has associated limitations. The accuracy of this method has not yet been sufficiently demonstrated for commercial viability. Factors such as edema, thick skin, hypothermia, obesity, which is a common factor in diabetes, or local blood flow changes may affect accuracy. There may still be discomfort associated with obtaining interstitial fluid as the skin barrier must still be penetrated. Finally, contaminants in such small samples would likely cause large variations in measurement accuracy.
A completely non-invasive approach would result in the largest improvement in patient compliance for monitoring blood glucose levels. Non-invasive blood glucose monitoring involves applying a radiation to tissue and measuring the interaction with glucose to determine the concentration. Promising optical-based technologies for noninvasive measurement of glucose concentration include near-infrared (NIR) light spectroscopy, mid-infrared radiation (MIR) spectroscopy, and optical rotation of polarized light. Examples of such non-invasive techniques and associated apparatuses are set forth in U.S. Pat. Nos. 5,703,364, 5,574,283, 5,460,177, 5,379,764, 5,360,004 and 5,077,476.
Although the use of NIR spectroscopy combined with the prudent use of chemometric techniques allow predictive models to be obtained that relate directly to the chemical spectroscopic signature, there are drawbacks to such approaches. There is the lack of repeatability of NIR measurements in vivo both within and between patients. The attendant signal variations are due in part to changes in the skin tissue optics between patients, the lack of a repeatable pathlength inherent in using a diffusely reflected photon approach, and temperature variations at the surface of the body. In addition, the pressure with which a probe is applied to the skin surface can play a major role in the predictive capability of the technique. None of the previous approaches to non-invasive glucose sensing have attempted to address these important issues of skin optics and pathlength that will inevitably have significant variation across the population of diabetics.
The present invention is therefore directed to a method and an apparatus for analyte detection which substantially overcomes one or more of the problems due to the limitations and disadvantages of the related art.
An object of the present invention is to provide an implant that would facilitate non-invasive optical measurements of analyte concentrations in the tissue, blood or interstitial space.
Another object of the present invention is to provide an infection-free implant that would eliminate problems related to skin optics by providing a window to the body that could be used with a variety of optical approaches such as near-infrared (NIR) absorption spectroscopy or optical rotation of polarized light to determine the concentration of the analyte.
A further object of the present invention is to provide an implant with a fixed optical pathlength minimizing variations inherent in previous approaches.
Yet another object of the present invention is to provide an implant to minimize variations in optical signals due to ambient temperature fluctuations.
An additional object of the present invention is to provide an implant to minimize probe movement during optical measurements.
Another object of the present invention to provide a rigid implant with a fixed optical window to minimize variations in optical signals due to the probe or the device.
Yet another object of the present invention is to provide an implant that demonstrates signal variations due to analytes in the blood thereby providing a direct measurement of the concentration in the blood.
Further objects and advantages are to provide an implant which can be used easily and conveniently by patients in their home, which is simple and inexpensive to manufacture, which can be used across a population of patients, which facilitates better patient compliance for monitoring important analytes in order to maintain normal blood concentration levels, and which obviates the need for acquiring a fluid sample to measure the concentration of an analyte in the blood.
At least one of the above and other objects of the present invention may be realized by providing an apparatus for facilitating measurement of analyte concentration including a housing, an optical window in the housing, the housing having a through portion downstream of the optical window in a path of optical radiation supplied to the window, an optical output portion, downstream of the through portion in the path of optical radiation, which outputs optical radiation transmitted through a sample in the through portion to an analysis unit, and a transcutaneous access device securing the housing to a subject.
The optical output portion may include a reflective surface directing the optical radiation back through the through portion and the optical window. The reflective surface may be shaped to focus the optical radiation back through the through portion and the optical window. The reflective surface may include an active optical coating. The reflective surface may include a biologically active mirror coating which promotes vascular ingrowth.
The optical window may focus the optical radiation onto the through portion. The through portion may include a porous wall structure which promotes vascular ingrowth. The through portion may include a porous wall structure which prevents vascular ingrowth, while allowing interstitial fluid to pass therethrough. The size of the through portion may be fixed. The housing may be recessed within the transcutaneous access device
The output optical portion may include another housing, another optical window in the another housing, the another optical window transmitting optical radiation generated by the sample in the through portion and another transcutaneous access portion in which the another housing is secured to the subject. The another optical window may be shaped to focus light passing therethrough.
At least one of the above and other objects of the present invention may be realized by providing system for measuring analyte concentration including a housing, an optical window in the housing, the housing having a through portion downstream of the optical window in the path of optical radiation supplied to the window, an optical output portion, downstream of the through portion in the path of optical radiation, which outputs optical radiation transmitted through a sample in the through portion, a transcutaneous access device holding the housing, an optical source for supplying optical radiation to the optical window, and a delivery system for supplying the optical radiation output by the optical output portion to instrumentation for analysis of analyte concentration.
The optical source may be one of an NIR source and a MIR source. The optical source may be fluorescence excitation within the housing. The optical source may be the body in which housing has been implanted.
At least one of the above and other objects of the present invention may be realized by providing a method of obtaining optical data for use in determining analyte concentration including implanting a transcutaneous access device in a subject, securing a sensor portion in the transcutaneous access device, the sensor portion including an optical window and a through portion downstream of the optical window in a path of optical radiation supplied to the optical window, providing optical radiation through the optical window to the through portion, and supplying optical radiation transmitted through a sample in the through portion, in response to the providing of the optical radiation, to instrumentation for determining a corresponding analyte concentration.
The supplying may include reflecting optical radiation transmitted by the sample in the through portion back through the through portion and the optical window. The supplying may include transmitting optical radiation transmitted by the sample in the through portion.
These and other objects of the present invention will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating the preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.